Koa web app framework

Expressive HTTP middleware for node.js to make web applications and APIs more enjoyable to write. Koa's middleware stack flows in a stack-like manner, allowing you to perform actions downstream then filter and manipulate the response upstream. Koa's use of generators also greatly increases the readability and robustness of your application.

Only methods that are common to nearly all HTTP servers are integrated directly into Koa's small ~550 SLOC codebase. This includes things like content negotiation, normalization of node inconsistencies, redirection, and a few others.

Koa is not bundled with any middleware.

$ npm install koa

Koa is supported in all versions of iojs without any flags.

To use Koa with node, you must be running node 0.12.0 or higher for generator and promise support, and must run node(1) with the --harmony-generators or --harmony flag.

  • Kick-Off-Koa - An intro to koa via a set of self-guided workshops.
  • Workshop - A workshop to learn the basics of koa, Express' spiritual successor.
  • Introduction Screencast - An introduction to installing and getting started with Koa
var koa = require('koa');
var app = koa();
// logger 
app.use(function *(next){
  var start = new Date;
  yield next;
  var ms = new Date - start;
  console.log('%s %s - %s', this.method, this.url, ms);
// response 
app.use(function *(){
  this.body = 'Hello World';
$ make test